The present invention relates to an automatic gain-controlled optical fiber amplifier, and, more particularly, to an erbium doped fiber ampliFier (EDFA) for use a multi-wavelength optical transmission system which maintain an output of each channel of the optical fiber amplifier regardless of a transmission line loss or a variation of a number of input channels and has a rapid speed and a simple structure.
Generally, the optical fiber amplifier amplifies directly an optical signal using an erbium doped fiber, and in present, is used diversely as a repeater and a switch element in a multi-wavelength optical transmission system.
The input power of the optical fiber amplifier is varied by various causes, such as a variation of transmission line loss and that of a number of input channels of the optical fiber amplifier due to network reconfiguration or using an optical add/drop multiplexer.
A conventional multi-wavelength optical transmission system is operated by point-to-point transmission method, thereby fixing the number of input channels of the optical fiber amplifier. Therefore, a variation of the input signal power of the optical fiber amplifier is only changed by a transmission line loss.
However, a multi-wavelength optical transmission system in accordance with the present invention is changed by point-to-multipoint transmission method, thereby changing the number of the input channels of the optical fiber amplifier because optical channels are added or dropped in each node.
Therefore, in order to use an optical fiber amplifier in a multi-wavelength optical transmission system of point-to-multipoint method, it has to recognize whether the variation of the input signal power of the optical fiber amplifier is caused by a transmission line loss or a changing of the number of the input channels and maintain constantly an output of each channel.
It is, therefore, an object of the present invention to provide an automatic gain-controlled optical fiber amplifier which maintains an output of each channel of the optical fiber amplifier regardless of a transmission line loss or a variation of a number of input channels and has a rapid speed and a simple structure.
It is another object of the present invention to provide an automatic gain-controlled optical fiber amplifier which measures a number of input channels by an input power of an optional channel signal and an amplified spontaneous emission (hereinafter, referred as xe2x80x9cASExe2x80x9d) noise from the output measured by using a wavelength selection filer and then, maintains an output of each channel of the optical fiber amplifier regardless of a transmission line loss or a variation of a number of input channels.
To achieve the above object, in accordance with one aspect of the present invention, there is provided an automatic gain-controlled optical fiber amplifier, comprising: a first optical branch for branching a portion of an optical signal inputted into the optical fiber amplifier; a second optical branch for branching a portion of an optical signal outputted from the optical fiber amplifier; a optical distributor for receiving the optical signal of an input side branched partially by the first optical branch and for outputting separately it; a first wavelength selector for receiving the optical signal of an one side distributed by the optical distributor and for selecting a predetermined wavelength optical signal; a second wavelength selector for receiving the optical signal of a output side branched partially by the second optical branch and for selecting the predetermined wavelength optical signal; a signal processor for receiving the optical signal of a second side distributed by the optical distributor and the predetermined wavelength optical signal selected by the first and second optical wavelength selector and for measuring a total power of an input signal and a number of input channels; a controller for generating a control signal according to the total power of the input signal and the number of input channels measured by the signal processor; and a optical amplifier and attenuator for outputting into the second optical branch by amplifying and attenuating the optical signal inputted from the first optical branch by means of the control signal of the controller.